1. Technical Field
The present invention relates to an atomic oscillator.
2. Related Art
An atomic oscillator in which transition energy of an atom is used as a reference frequency is widely used in a communication base station or the like as one of the most accurate oscillators. There are several types of atomic oscillators, and a microwave dual resonant type atomic oscillator using a rubidium (Rb) lamp is generally used the most.
Recently, an atomic oscillator using a phenomenon referred to as Coherent Population Trapping (CPT) which is one of quantum interference effects is proposed (for example, refer to JP-A-2009-89116), and thus a reduction in the size of the atomic oscillator and low power consumption are expected compared to the related art. In a case of a CPT type atomic oscillator, a high frequency signal is superimposed by using a coherent light source such as a laser as a light source, and thus a side band thereof is used in the expression of the CPT phenomenon. The CPT type atomic oscillator is an oscillator using an Electromagnetically Induced Transparency phenomenon (an EIT phenomenon) which stops absorption of light coherent when an alkali metal atom is irradiated with the coherent light having two different wavelengths (frequencies).
In the CPT type atomic oscillator, in general, a central frequency of laser light with which the gas cell is irradiated is controlled in order to increase a frequency stability degree of the atomic oscillator. The central frequency of the laser light is controlled by changing a bias current of the laser.
However, in the above-described atomic oscillator, the bias current of the laser is changed in order to control the central frequency of the laser light, and thus a light quantity of the laser is changed. For this reason, in the above-described atomic oscillator, a light shift (a phenomenon in which a resonant frequency is changed due to an AC stark effect) may occur.